Sound record producing apparatus



y 1943- E. w. KELLOGG 2,323,606

7 SOUND RECORD PRODUCING APPARATUS Filed June 24, 1939 Zinoentor Patented July 6, 1 943 I v srara 2,323,6@6 SGUND, RECORD PRODUCING APPARATUS Edward W. Kellogg, Moorestown, N. 3., assignor to Re Corporation of erica, a corporation of Delaware 1 Application June 24,1939, Serial No. 280,960 1 Claim. (oi. ire-loos) .is required or where a record of great density is required to be produced of a relatively slow film, it is necessary to use a high intensity light source in order to secure suiiicient illumination. One type of such light source which is now available i known as the high pressure mercury vapor lamp, and operates at a. mercury vapor pressure of from several to many atmospheres. Likewise, it maybe desirable occasionally to use the more conventional type of mercury-vapor lamp operating at a pressure of the order of one atmosphere for reasons of color sensitivity or the like, although this latter type of lamp does not have nearly as high an intrinsic brilliancy as the type above referred to.

It is characteristic of all mercury vapor lamps that after they are started, it requires a, relative long time, of the order, for example, of from 5 to 10 minutes, for them to reach constant brilliancy. This is due to the fact that the envelope becomes gradually heated, and until equilibrium with the surrounding air is reached, the rate of condensation of the mercury is continually changing and, therefore, the vapor pressure does not become constant. Likewise, if during operation of the lamp the current therethrough is changed, it again requires a long time until the light becomes truly constant. For example, if the resistance in series with such a lamp is reduced, the current throughthe lamp rises, and the light radiated increases, but does not immediately assume its ultimate value. The current drops slowly back from the value immediately following the decreasev in, series resistance, and .the voltage slowly increases as the final temperature is approached. During thisperiod of chan g bulb temperature, the radiation undergoes more or less change. Therefore, when considerable precision of adjustment in light intensity is required, and

where valuable time may be lost if the desired value of light cannot be obtained immediately,

the method oi adjusting the supplied voltage or serie resistance is not satisfactory.

- In making photographic so records, forexample, either by recording-or ting, it is necessary to maintain the exposure at a predetennined value within fairly close limits, and it is impractical to accomplish this by adjusting the lamp current for the reasons just given.

. In the performance of my invention, 1 use a mercury vapor lamp or lamp of 1:101 chamoteristics and place the operating current at a suificiently high value for adequate exposure. After the lamp has reached equilibrium, the light intensity is adjusted to an appropriate value throughthe use of a variable density wedge, or by Another object of the invention is to provide an improved apparatus for controllingthe intensity of the sound recording or printing light. Another object of the invention is to provide means for controlling the light reaching the film from a light source which i not directly controllable.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and the accompanying drawing, in which 7 'Figure 1 is a diagratic, perspective view of a sound recording optical system made in accordanoe with my invention, and

Figure 2 is a diagrtic, perspective View of a modified form or the invention.

Referring to Fig. 1: i The light source of the type referred to above which may -be, for example, the type of lamp known as the General Electric Company type H3, is indicated at 50. Light from the source it passes through the condenser lens it which through the aperture falls upon the lens ii which.

in conjunction with the lens H, focuses an image of. the light source it upon the galter mirror iii. This galvanometer mirror is ted about a transverse axis in accordance with the sound or other vibrations'to be recorded. t reflected from themirror it the lens ii to the slit iste t8. Lenses is is together locus an image of the as in the plate l2 upon the slit plate ll snap '1- I ortion of this image as through the slit l9 and is focused upon i in the l is toprovide an form of a narrow line by the objective lenses 20 and 2|.

In order to control the intensity of the light reaching the film F, I insert a variable density wedge 22 adjacent the slit ID. This wedge may be formed in any of the known ways for producing such a device. It may, for example, be a wedge-shaped piece of dark glass, or it may be produced by exposing a photographic plate in continuously greater degree from one ed e to the other, or by other well known methods of progressively greater light absorption across a transparent plate.

After the light In is turned on and has reached I equilibrium, the brightness of the light reaching the film F is determined by a test exposure or photometrically as, for example, by the apparatus described and claimed in Zimmerman Patent No. 2,233,907, issued March 4, 1941. The wedge 22 is then moved vertically, i. e. transversely, relativeto the slit, as shown in the drawing until the desired light value is reached. The wedge 22, it must be understoodi at any position of uniform density throughout. the length of the slit, but of graded density in the vertical direction.

It will be apparent that this adjustment can be accomplished practically instantaneously and that since the intensity of the source I0 is not varied, there is no delay involved in waiting for the system to reach equilibrium.

Another form of the invention is shown in Fig. 2, in which corresponding parts are rep resented by the same reference numerals as in Fig. 1. This figure omits the portions from the lens IE to and including the lamp Hi, all of which portions remain the same as in Fig, l. The form of the invention shown in this figure differs from that shown in Fig. 1, in that the iris diaphragm 23 located between the objective lens elements 20 and 2| is substituted for the variable density wedge 22.

This diaphragm 23 serves the same purpose 'as the movable wedge 22 of Fig. l, but performs its function by varying the size of the circular aperture at its center, which aperture controls the exposure of the film in exactly the same manner as a camera aperture or diaphragm controls exposure. It is obvious that-the wedge 22 in Fig. 1

might be interposed in the path of the light at some other point than adjacent to the slit l9, but it is essential for best results that it shall not cause the intensity of illumination of the slit I9 to vary as a'result of movements of the galvanometer mirror It. Thus, it might be located almost anywhere between the mirror l6 and the film F, but it should not be located between the lamp IO and the mirror l6, unless it can be substantially adjacent to one or the other of these. In the case of Fig. 2, the variable aperture should not be located where it will impair the uniiormity oi illumination of the slit l9, or of the image thereof on the film. This condition practically limits the location of the diaphragm to a position substantially adjacent to the lamp I 0, or adjacent to the mirror l6, or adjacent to or within the objective lens system, as shown. These are points known as aperture stops in the system, where the area of the opening determines the intensity ofthe light, and in the case of the optical system illustrated herein, are either at the light source itseli. or

at an optical image thereof.

It will be obvious that the variable area ope ing employed in Fig. 2 need not necessarily be circular in tom, and might be provided by any of numerous possible arrangements of movable vanes.

It will be apparent to those skilled in the art that my invention is not limited to the use of a mercuryvapor lamp either of the high pressure type or of the conventional type and that it is equally applicable to any other type of lamp requiring a considerable length of time to reach a steady condition, or to any application in which control by changing lamp current is objectionable for any reason whatever. This characteristic of the mercury lamp, which makes the control by the method of my invention, is noticeable in metallic vapor lamps in general including 'those'using the vapors of other metals such as sodium or potassium, as well as mercury. Other applications assigned to the same assignee on the same general subject matter as the present application are Dimmick Patent No. 2,265,103, issued Dec, 2, 1941, covering the location of the adjusting means at an aperture stop of the optical system and particularly adjacent the galvanometer mirror, and Sachtleben application Serial No. 281,951, filed June 29, 1939, issued Dec. 24, 1940, as Patent No. 2,225,714, covering the specific type of adjusting mechanism for a diaphragm located in the galvanometer.

Having now described my invention, I claim: In combination, a variable area sound film recording optical system including a mercury vapor light source and a series of lenses adapted to focus a fine line of light from said source upon a film, means including a light slit element for modulating the light from said source in accordanee with sound to be recorded, and alight wedge disposed in the path of said modulated light between said light slit'and said film for adjusting the average intensity of said modulatd light beam independently of said light modulating means. EDWARD W. KEIJLOGG. 

